1. Field of the Invention
The present invention relates generally to the art of rotary web printing, and more particularly to a web printing press having a web metering system for controlling the speed of a web through the press.
2. Discussion of the Prior Art
Flexographic web printing presses are conventionally used in the printing of a wide variety of materials such as packaging and the like, and typically include a plurality of printing units, each provided with a flexographic plate cylinder, an impression cylinder opposing the plate cylinder to form a printing nip, and an inking assembly including an anilox roller for inking the plate cylinder. In addition, conventional presses may include downstream web handling equipment such as one or more die units, slotters or the like for preparing the web material for use.
It is conventional to provide a single motor-driven line shaft on a flexographic web printing press for driving rotation of the printing units. A gearbox is provided between the line shaft and each unit for driving the plate cylinder, anilox roller and impression cylinder during printing. In addition, the line shaft drives one or more web feed rollers associated with each printing unit to advance the web through the press.
Known flexographic web printing presses are initially set up to handle webs of a predetermined thickness, and are not easily converted to handle webs of a thickness differing substantially from the predetermined one. Because the print length of any particular web substrate is measured at the center line intermediate the opposed surfaces, a thin material requires a shorter web length than a relatively thick material. It is not possible in conventional presses, without significant set up or change over, to adjust the web feed rollers and guide rollers to accommodate such dramatic changes in web thickness. For example, if a press is originally set up to handle relatively thin webs, such as plastic film stock used in the manufacture of labels and the like, it is not possible to easily convert the press for use in printing thick webs such as are used in the production of popcorn boxes or other heavy packaging materials.